No Dvd Collection should be missing the Alien Quadrilogy Boxset! Not only do you get 2 versions of each film but also an extra 5 discs of special features!
The films vary in terms of quality. Ridley Scott's fantastic Alien (1979) starts it all off, now you can watch the 2003 Director's Cut which is actually shorter than the theatrical release, mainly for pacing reasons, however it also includes new footage previously unseen. The film is fantastic, extremely suspenseful and claustrophobic with a brillaint cast.
James Cameron carried on the Alien legacy in Aliens (1986) and decided "This Time It's War!" The film is extremely action orientated while still sticking to the feel of the original making it immensely entertaining! For best results watch the Special Edition for around half an hour of extra footage such as cool century guns!
In 1992 Alien3 was released to generally negative reviews and poor fan reactions. Forget what you think you know about Alien3! The David Fincher directed third installment is best seen in the extended cut, also known as the assembley cut which is wildly different from the original film and 10 times as good, to learn more and get a full understanding on this underated film watch the special features to learn of the troubled production and general problems with the movie. Trust me it will give you a new respect and understanding.
Alien Ressurection (1997) closes off the saga. Unfortunately Jean-Pierre Jeunet fails to make a film as entertaining as the previous 3 directors and even casting Winona Ryder alongside Sigourney Weaver does little to boost this mishmash of a film, generally it leaves a bad taste in your mouth, the only enjoyment I got from this film was seeing 2 brillaint actors (Ron Perlman and Sigourney Weaver) playing off each other very well.
Overall don't let the poor 4th installment put you off, this boxset is fantastic and well worth the price, there are loads of extras to educate you on the entire production and history of the Alien Quadrilogy!